Communication in the depths: perhaps not as primitive as we would like to think – Coleoid communication.

Have you ever wondered how animals communicate? Some animals have incredibly complex behaviour, and in many cases communication is a vital part of that behaviour. I have recently been researching communication in Coleoids and I wanted to demonstrate to you all how complex, and beautiful in its complexity this communication is.
First of all, what are Coleoids? Coleoids are Octopus, Cuttlefish and Squid. In these animals the most dominant form of communication is visual communication, using chromatophores. Chromatophores are very small sacs of pigment granules. Upon contraction, muscle surrounding each pigment sac draws the sac out into a pigment sheet. Each chromatophore can be individually controlled, allowing for very fine adjustment in the display pattern. Although very small, the cumulative effect of these pigment sheets results in the incredible patterning seen in the Coleoids.

Figure 1 - Intense Zebra display in Cuttlefish

There is a huge diversity of patterns the Coleoids use to communicate a wide variety of information. Obviously we will never know for sure exactly what information these animals are conveying, but through observational studies researchers can infer meaning upon a pattern. One of the most well-known patterns is the Intense Zebra display shown above. This cuttlefish has zebra bands, a dark eye ring, white fin line and white arm spots. It may not seem (sexually) appealing to you or I, but this is actually a signal used by males to signal to females they want to mate. Sometimes, while mating the male needs to both keep the female interested (with the Intense Zebra display) and warn off any other males. To do this the Coleoids have an incredible ability to show one signal on one side of their body, and another completely different signal on the other side of their body. In this case a signal of aggression – deimatic signalling. Deimatic signalling is the sudden appearance of dark or bold chromatic components. These dark or bold chromatic components can be seen in the image below. A type of deimatic signalling not mentioned in the above image is the display of false eye spots. The final picture in this post is an extreme example – the blue ringed octopus. This animal displays a large number of eyespots presumably to intimidate a predator – “look at how many of me there are” etc.

Figure 2 - Deimatic signalling

While only sexual and deimatic displays have been discussed here, there are a huge variety of displays in the Coleoids. The communication system in these animals is undoubtedly complex, as shown in the elegant chromatophore mechanism. (The eye and brain contributions to this system are of equal importance, but not covered in this post for simplicity). Despite many years of research on the communication in these animals there are many questions still to answer. Future research should look at the development of communication in these animals, as well as the costs and benefits of signalling. Answering these questions may help us to understand why these invertebrates evolved such a sophisticated mechanism for communication.